Among the various commercial processes practiced, an important one involves the physical or chemical treatment of hydrocarbons and other organic materials with bodies of granular contact material. Frequently such a process involves contacting a two-phase mixture of liquid and vapor with the contacting material and the introduction of such mixtures into the bed of granular contact material in a uniformly distributed manner.
Uniform distribution of a liquid and vapor into a granular bed of contact material is a difficult goal to achieve. In a typical process a vapor-liquid feed material is introduced into a vessel which is divided into an upper and lower portion by one or more distribution trays. The distribution trays are provided with a number of overflow weirs, or the like, and provide the sole means of fluid communication between the upper portion of the vessel and the lower portion of the vessel, the latter of which contains a bed of the granular contact material.
The feed mixture is introduced into the upper portion of the vessel and the liquid collects in a pool or reservoir on the tray from whence it flows over the rims of the weir into the bed of contact material. An inherent disadvantage of such an approach is that the methods of fabrication normally employed in the construction of reactors are not sufficiently precise to ensure an absence of irregularities (differences in the outlet weir elevation, tilting of the weir, tilting of the distribution tray, etc.) in the reactor. In addition the operating conditions within the reactor are frequently such as to bring about distribution tray warping, thus contributing to even more irregularities. As a result, some of the outlets will inevitably exhibit little or no overflow of liquid feed.
It has been proposed to provide slots or V-notches in the weir to minimize the effect of these irregularities. Such proposals have not eliminated the problems associated with irregular flow. Further, the liquid feeds have a tendency to channel down the inner surface of the outlet weir and impinge upon the catalyst bed in relatively thin streams which bury themselves deep in the bed before spreading laterally to any significant extent.
The more common practice is the use of a "bubble cap" assembly. A bubble cap assembly is disposed over each of a plurality of openings in the distribution tray. Each bubble cap assembly comprises a riser portion, generally having the shape of a hollow conduit, and a cap portion which is spaced apart from the riser forming an inverted U shaped flow path for the vapor and liquid. In most designs the cap portion may have a plurality of slots in its lower most outer periphery to accommodate irregularities of the type described above, and variations in liquid flow rates. Such designs have met with commercial success. Nonetheless, there is still need for improvement. It must be appreciated that even a one or two percent increase in yield, which could be obtained by more uniform distribution of the liquid-vapor upon the particulate bed, could amount to millions of dollars per year in, for example, a petroleum refining operation.